There’s a maturity cycle that tanks progress through. One of the marks of a mature, experienced tank is they know the encounters and they plan ahead. Newer tanks are usually focused on their action-bars and rune cooldowns, on the mechanics of acting. Mature tanks handle the basic threat actions without much conscious focus, and instead expand their awareness to the whole game field, and planning for what’s coming up next.
One thing paladins enjoy is a fairly consistent action of 969 to keep up the threat. Whilst DKs can definitely settle into a routine, it is generally more stabby and less flowing. Having sensible keybindings helps with flow.
Example: the arena phase in Thorim (Ulduar) can be handled by a DK if they’re not burning off all their runes, and instead keeping some in reserve for the next wave. If a DK uses up runes to overly strike the target, they’d be handicapped for the next wave with a worst-case of having to auto-attack.
Planning ahead in this scenario translates to not using up your runes, because you know they’ll be needed to get agro on the next spawn.
DKs can use blood tap and empower rune weapon as ‘get out of jail’ cards (so their big tank cooldown can still be used), but ideally you’d have planned ahead and have the appropriate rune ready to use.
The skill is balancing this conservation against the threat you need to stay ahead of the dps, thus not sitting on a rune for overly long, and the sign of maturity is balancing all these factors whilst observing the whole game field and your own health bar.